1. Field of the Invention
The present invention relates to an imaging apparatus, and, more particularly, to a method of media type sensing for an imaging apparatus.
2. Description of the Related Art
Media sensors are used to detect the presence or absence of print media, and in some cases, are also used to determine the print media type. One form of a media sensor includes a single light source, such as a light emitting diode (LED), and a light detector, such as a phototransistor. Typically, the light detector is located on the same side of a print media as the light source. During operation, the LED directs light at a predefined angle onto a material surface of the print media, and the surface characteristics of the print media are examined in terms of the amount of light reflected from the surface that is received by the light detector. For example, the presence of the print media is detected based upon a predetermined amount of light reflected from the media to the light detector.
One known sensor is a photo sensor that responds to a first reference spectral reflection from a reference surface at an angle of reflection equal to the angle of incidence. When a sheet of media is registered by the printer against the reference surface, the photo sensor responds to a second spectral reflection from the sheet of media. The ratio of the second spectral reflection intensity to first spectral reflection intensity is compared to a selected threshold to identify the media by gloss level.
It is further known to have a detection system in which external light is detected during a non-emission state of a light emitting element and is used to correct a reference value. The corrected reference value is then compared to a detected value of light emitted from the light emitting element and reflecting from an original to be copied, and based on the comparison a determination is made as to the presence of an original.
Some media sensors include a pair of light detectors, one of the light detectors being positioned to sense reflected diffuse light and a second detector positioned to sense reflected specular light. Such a sensor may be used, for example, to detect and distinguish between various media types by optically measuring the glossiness of the media based on each of reflected specular light and reflected diffusely scattered light. To measure the glossiness, a collimated beam of light is directed towards the media and a reflectance ratio (R) of the detected reflected specular light intensity and the detected diffusively scattered light intensity is calculated. The media sensor is initially calibrated by measuring a reflectance ratio (R0) on a known gloss media. A normalized reflectance ratio (Rn) is calculated using the formula: Rn=(R/R0). Normalized reflectance ratio Rn then is used to identify the media type of an unknown media by a comparison of the normalized reflectance ratio Rn to a plurality of normalized reflectance ratio Rn ranges, each range being associated with a particular type of media.
What is needed in the art is an improved media sensing system and method that can use a simple single detector sensor using low cost digital electronics, and which reliably distinguishes between various media types.